ENDOPHYTIC ALGAE OF CHONDRUS-CRISPUS (RHODOPHYTA) .3. HOST SPECIFICITY

Susceptibility of rhodophycean macroalgae to infection by the green endophytes, Acrochaete operculata Correa & Nielsen and A. heteroclada Correa & Nielsen was studied. Cross-infection experiments showed that A. operculata is host specific and developed only in sporophytic fronds of Chondrus crispus Stackh. and Iridaea cordata (Turn.) Bory. Although A. operculata penetrated equally the multilamellar outer cell wall of sporophytic and gametophytic fronds of C. crispus, subsequent development was arrested in the gametophytic fronds. Susceptibility of the sporophytic phase of C. crispus was detected early in the development of the host, at a discoid stage that is structurally distinct from the adult fronds. The evidence strongly suggests that host specificity in A. operculata is determined by cell-wall composition of the hosts, likely the carrageenan fraction. In contrast, A. heteroclada was not host specific, infecting all offered hosts, including carrageenophytes and agarophytes. Germination occurred on the surface of the hosts and led to the development of an epiphytic stage. Subsequent penetration in many cases involved total displacement of cortical tissue in the infected frond.